The present invention relates to a circuit breaker such as a molded-case circuit breaker or an earth leakage breaker. Particularly, the invention relates to an assembly structure of a molded case containing functional parts of the breaker.
As known, a molded-case circuit breaker incorporates contactor sections, each including a stationary contactor and a movable contactor of a main circuit, arc-extinguishing devices for the respective contactor sections, a switching mechanism for the movable contactors, and an overcurrent tripping device, which are assembled together in a molded case. Moreover, an earth leakage breaker includes, besides functional parts making up a molded-case circuit breaker, a leakage current detection section (a zero-phase current transformer and a leakage current detection circuit) and an over current protection device additionally installed in a molded case (see Japanese Patent No. 3246562, for example).
In the circuit breaker with the above arrangement, interruption of an overcurrent such as a short-circuit current causes an arc to occur between a stationary contact and a movable contact in the main circuit. The heat of the arc causes contactors made of metal to melt and evaporate. The evaporated molten metals scatter with arc gas and deposits onto movable parts of the switching mechanism and the tripping device, which causes interruption in the function. Thus, as a measure for preventing the problem, the following structure is known (see JP-A-7-141976, for example). In the structure, an intermediate base is incorporated inside a molded case so that a current interruption section and an arc-extinguishing device are isolated from the switching mechanism arranged above them with the intermediate base serving as a partition wall.
In addition, a circuit breaker having other attachments is known. In the structure, for allowing easy mounting of the attachments of the circuit breaker such as an auxiliary switch, an alarm switch, and shunt release, pocket-like recesses are formed beforehand on the cover of a molded case. In the recess, the attachment is retained in cassette form and an auxiliary cover is provided to cover the top sides of the attachments (see JP-A-6-236726, for example).
Aside from the structure disclosed in JP-A-7-141976 in which an intermediate base is incorporated inside a molded case, a circuit breaker with the following assembly structure was already developed and commercialized. In the assembly structure, a molded case is designed to isolate the switching mechanism from the current interruption section that has capability of containing interior attachments like the molded case disclosed in JP-A-6-2367276. The molded case has a structure of three parts, which are a main case (lower cover), a middle cover laid on the top side of the main case with a recess, partitioned by a bottom wall, formed in its central section, and a top cover covering the top side of the recess in the middle cover. The contactor sections, the arc-extinguishing device, and the overcurrent tripping device are contained in the main case. The switching mechanism and interior attachments are contained in the recess in the middle cover. In the following, the assembly structure of the circuit breaker is shown in FIG. 4.
In FIG. 4, reference numeral 1 denotes the molded case (a resin molded product) with the structure dividable into three parts, i.e. the main case (a lower case) 2, the middle cover 3 and the top cover 4. Reference numerals 5, 6, 7 and 8 denote a stationary contactor integrated with a power supply side terminal, a load side terminal, a movable contactor, and a contactor holder rotatably supporting the movable contactor 7, respectively. Reference numeral 9 denotes the arc-extinguishing device. Reference numerals 10, 10a and 11 denote the switching mechanism of a toggle link type, a switching operation lever, and a tripping mechanism linked to the toggle link of the switching mechanism 10, respectively.
Reference numeral 12 denotes an overcurrent tripping device that detects an overcurrent in a main circuit to actuate the tripping mechanism 11, and reference numeral 13 denotes a zero-phase current transformer mounted in an earth leakage breaker for detecting a leak current in the main circuit. The zero-phase current transformer 13 has a leak current detection IC connected to the secondary side to form a leak current detection section. The switching operation and the current interruption operation of the circuit breaker are known, so explanations are omitted.
Here, in the main case 2 of the molded case 1, units, each including the stationary contactor 5, the movable contactor 7, and the arc-extinguishing device 9 for each of the phases of the main circuit, are contained parallel in the lateral direction. On the back of the units, the overcurrent tripping device (thermal device) 12 and the zero-phase current transformer 13 on the further back are arranged between the load side terminals 6.
Moreover, the middle cover 3 laid on the main case 2 has a pocket-like recess 3a formed at the central section with a wall provided around the recess 3a for partitioning. The recess 3a is provided so that the switching mechanism 10 and the tripping mechanism 11 are contained in the middle. The previously described overcurrent protection device of the earth leakage breaker and the interior attachments (not shown) such as the auxiliary switch, the alarm switch, and the shunt release are contained on the side of the recess 3a. Furthermore, through a slit opened in a bottom wall 3b of the recess 3a, a lower toggle link 10b of the switching mechanism 10 is made to project downward to couple with the contactor holder 8 of the movable contactor 7.
Further, on the top side of the middle cover 3, the top cover 4 is mounted to cover the top side of the recess 3. The top cover 4 has an opening at the center so that the switching operation lever 10a of the switching mechanism 10 is made to project outside through that opening.
The circuit breaker described above with background structures has the following problems from the viewpoint of easiness in maintenance and assembly. Namely, devices such as the auxiliary switch, the alarm switch and the shunt release as the attachments of the circuit breaker are often mounted by a user after the circuit breaker is delivered. In this case, mounting and removal of the attachments are carried out by making access to the recess 3a in the middle cover 3 with the top cover 4 shown in FIG. 4 being removed. At the access, danger of injury arises such as an accidental touch of a fingertip of a worker on the tripping mechanism 11 in the switching mechanism 10. This causes an unexpected tripping action of the switching mechanism, by which the finger of the worker is pinched.
In addition, in the assembly process of the earth leakage breaker, with the functional parts that make up the molded-case circuit breaker being assembled in the main case 2, the zero-phase current transformer 13 (the leakage current detection section) is mounted. Furthermore, in addition to mounting on the middle cover 3 equipped with the switching mechanism 10 and the overcurrent protection circuit, on the main case 2, lead wires taken out from the leakage current detection section are connected to the overcurrent protection device mounted in the middle cover 3. The wiring carried out with the switching 10 being exposed will cause an unexpected tripping action of the switching mechanism as described above, resulting in a finger pinched in the switching mechanism.
The invention was made in view of the foregoing, and an object of the invention is to provide a circuit breaker with the structure of a molded case based on the structure shown in FIG. 4 with improvement on easiness in assembly and maintenance.